Plastic milling apparatus



Feb. 27, 1951 H. A. SWALLOW ET AL PLASTIC MILLING APPARATUS 4 Sheets-Sheet 1 Filed Aug. 6, 1948 LOW H. ANDERSON INVENTORS T A. SWAL TTOREY 11" f A I I i HERBER Jig! HENRY Feb. 27, 1951 H. A. SWALLOW ET AL PLASTIC MILLING APPARATUS 4 Sheets-Sheet 2 Filed Aug. 6, 1948 ATTRNY 1951 l H. A. SWALLOW ET AL 2,543,307

PLASTIC MILLING APPARATUS INVENTORS HERBERT A. SWALLOW HENRY H. ANDERSON ATTORNEY Feb. 27, 1951 H. A. SWALLOW ET AL PLASTIC MILLING APPARATUS 4 Sheets-Sheet 4 Filed Aug. 6, 1948 ATTORNEY Patented Feb. 27, 1951 D STATES PATEN FF 1 C PLASTIC MlILLKNG APPARATUS Application August 6, 1948, Serial No. 42,778

6 Claims.

lhis invention relates to continuous milling and dosing of plastic material, including thermoplastic and thermosetting resins, and compositions of such resins that contain fillers, plasticizers, pigments or other additions, and apparatus suitable therefor.

Heretofore it has been common practice to mill, mix, or flux plastic materials and compo sitions containing them on heated two-roll mills or in Banbury mixers. These procedures are essentially batch operations, since in the instance of two-roll mills a charge of plastic material more than sufiicient to encircle after melting or fiuxing one of the rolls is placed in the nip or bite of the rolls; during the milling the charge forms as a sheet about one of the rolls, and after the charge is sufficiently milled, the sheet is stripped. With a Banbury mixer, a charge is loaded therein, mixed, and then dumped. Neither apparatus and procedure are entirely satisfactory because in successive batches unavoidable variations occur in operating temperatures and in the mixing, fluxing and milling.

A process and apparatus for continuous milling or mixing of plastic materials is shown and claimed in U. S. Patent 2 434,707 issued January 20, 1948, to W. R. Marshall, the proper functionof which depends on a radial clearance, in excess of mechanical clearance in the zone or intermesh between two V-type screw threaded rolls rotating in opposite irections through which the plastic passes. Such radial clearance oiiers no difficulty to the processing of plastic materials that 'are introduced to the apparatus as wet, viscous, or fiuxed masses, and so adhere or cling to the helical threads and the grooves between the threads. But when. uniiuxed granular or powdered material, such as comminuted resins, pigment matter or fillers, is fed into the lriarshall apparatus, these particles of material smaller size than the radial clearance tend to drop through the zone of intermesh. Some of the particles are picked up by subsequent contact with material that has been fluxed and is adhering to the threaded roll surfaces to be milled and rluxed therewith. The remainder of the particles fail to be subjected to the milling or flexing action of the intermeshing rolls and are discharged in an unaltered condition from the apparatus.

The present invention is directed to improvements of the continuous milling apparatus described in U. S. Patent No. 2&33'107, and it is particularly concerned with satisfactory continucus fluxing and milling of plastic materials introduced to the apparatus in granular, comminuted or finely subdivided form. The improved continuous milling apparatus of this invention is based on a pair of intermeshing ll-type screw threaded rolls rotating in opposite directions within a closely confining housing, with the modification that the threads of each roll are interrupted by at least one non-helical annular section, or surface of revolution having a diameter the same as or less than the outer diameter of the screw threads, each annular section mating with the other and each cooperating with a semi-circumferential barrier projecting from the housing bore toward said surface of revolution, to form therewith a devious, tortuous passageway having a width of more than mechanical clearance. Unfiuxed powdered plastic material, while being pushed through a devious passageway between such surface of revolution and projecting barrier, is pressed into intimate contact with previously fiuxed material and intensively admixed therewith, by being subjected to multiple forces comprising pressing, shearing, and tearing actions, whereby the unfiuxed material is completely fiuxed and admixed with previously fiuxed material before emerging from the restricted passageway for further milling and conveying by the intermeshing threaded rolls.

A. further improvement of theinvention comprises a continuous milling apparatus having a pair of intermeshing, J-type, screw-threaded rolls, each roll having a dual-thread, for instance, a right hand thread starting at one of the shaft ends of the roll and terminating about the longi tudinal center or mid axial length of the roll to form. a junction thereat with a left hand thread beginning there and terminating at the other shaft end of the roll. The dual-threaded rolls ar supported by bearings solely at their shaft ends. Plastic material fed into such an apparatus at the mid-juncticn of the dual-threads is completely milled and fiuxed upon reaching either shaft ends of the intermeshing rolls for discharge, without the plastic material having an opportunity to come into contact with or be entrapped by the bearings supporting the rolls.

These and other features of the invention are illustrated in the accompanying drawing in which Fig. 1 is a side elevation of a continuous milling apparatus having a positive feeding hopper for supplying plastic material at the mid-axial length of a air of intermcshing dual-threaded rolls enclosed within the apparatus;

Fig. 2 is a vertical section taken on the line 2-2 of Fig. 1;

Fig. 3 is a vertical section taken on the line 33 of Fig. 1 showing a rotating cut-off wheel assembly for cutting into strip form the milled material discharged from threaded portions of the rolls onto smooth surfaces of the rolls;

Fig. i is a vertical section showing a cutter- ;olcw knife modification for removing milled plastic material discharged onto smooth surfaces of the rolls;

Fig. 5 is a horizontal section taken along the line 5-5'of Fig. 1;

Fig. 6 is a detailed perspective view of a matching pair of semi-circumferential housing inserts having V-shaped non-helical barriers;

Fig. 7 is a fragmentary longitudinal section showing a driving dual left and right handed threaded roll, each thread being interrupted by an annular non-helical surface of revolution which is associated with the non-helical barriers of the semi-circumferential annular inserts shown in Fig. 6;

Fig. 8 is a fragmentary longitudinal section.

showing a driving dual- (left and right hand) threaded roll having in its center section a smooth annular surface of revolution, which is associated with V-shaped helical barriers positioned as an insert in saddle plates housing the dual threaded roll;

Fig. 9 is a detailed perspective view'of a matching pair of semi-circumferential inserts having interior projecting helical V-shaped barriers, previously shown in assembly with a housing in Fig.- 8;

Fig. 10 is a fragmentary longitudinal section showing a driving dual-(left and right hand) threaded roll embodying in one roll the two annular surfaces of revolution modifications shown in Figs. 7 and 8;

Fig. 11 is a view similar to Fig. 10 showing a dual-threaded roll having annular surfaces of revolution associated with annular and helical barriers formed integral with a housing confining intermeshing dual-threaded rolls;

Fig. 12 is a partial plan view showing a modified discharge surface on the end of the intermeshing threaded rolls for discharging a sheet having a ribbed or corrugated surface; and

Fig. 13 is a detail perspective View showing a portion of a corrugated sheet of plastic material formed by the discharge means shown in Fig. 12.v

Referring now to the embodiment shown in Figs. 1 to '7 of the drawing, there is mounted on a base a housing for a pair of intermeshing -type threaded rolls, said housing comprising jacketed. upper and lower saddle plates I9, constructed of metal and suitably fastened together. by eye bolts for maintenance convenience. The saddle plates, |9, 20 as shown in Fig. 2 form a closely confining smooth wall, dual-bore hous" ing for enclosing up to the zone of intermesh a pair of inter-meshing dual-threaded rolls 2|, 22 of cast iron. stainless, steel or other constructional material of adequate strength and resistance to corrosion and abrasion. Half of the axial length of each roll has a left-hand or counter clockwise V-type. thread and the other half has a right-hand or. clockwise V-type, thread, both threads terminating at a junction in the mid axial length ofthe roll. When positioned in the apparatus, the left hand thread of. one roll meshes with the right hand thread of the other roll, and;

the right hand thread of the first roll meshes correspondingly with the left hand thread of the second roll.

The threaded rolls 2|, 22 lie with their axes in a horizontal plane and are supported at their shaft ends by bearings 25, 26 and 21 positioned in bearing supports 28, 28, mounted on the base ID. The driving threaded roll 22 has an ex.- tended shaft 30 for coupling to a driving motor (not shown) for rotation in a counter clockwise direction. The"driving roll 22 by means of gears SI, 32 fastened to shaft extensions at the left end of each threaded roll 2|, 22, in turn cause the driven roll 2| to be positively rotated in a clockwise direction at the, same peripheral speed as the driving roll 22.

Interior semi-annular slots or recesses 34, 35 are formed in the saddle plates |9, 28 and in each recess is bolted a pair of semi-annular metal inserts 36, 12 having projecting non-helical barriers. The paired insert assembly 35 for the left side of the apparatus is constructed in four sections, 37o; Slb, 38a, 33b for easier installation and is shown in detail in Fig. 6. If 6 is rotated 180" on ho :al axis. it ould illus -etc the insert assembly 42 as installed on the right side of the apparatus. Each pair of semi-annular inserts 36, 52 has two inwardly projecting nonhelical, semi-annular V-shaped projections or barriers 29, 4|. The barriers 40, 4| of one of the pairs of the insert assemblies 38, G2 are in staggered relationship as to the barriers of the other in the paired assembly, to accommodate correspondingly staggered V shaped annular surface of revolution f. 4'5 on the intermeshing threaded rolls 2|, 22. The annular surfaces of revolution 52, M, rotate in the grooves 45 between the projecting semi-annular barriers 25, 4| on the insert assemblies 33, 42. The radial clearances between the staggered annular surfaces of revolution in zone of intermesh as well as the clearances between each annular of revolution Q3, 45-, t5, 4? and the grooves of its corresponding inserts 42 are more than mechanics. clearance to provide a space passage therethrough of material being milled and conveyed.

The saddle plate housings have jackets for introduction therein of cooling or heating fluids. The threaded rolls 2 I, 22 as shown in Fig. 5 have cores Z3, 29, to permit cooling or heating fluid to be circulated in the interior of the threaded rolls 2 22 as operating conditions require.

The discharge ends of each threaded roll 2|, 22 are provided with smooth annular slu'faces 55, 52 against which are pressed plow cutter shaped knives 5d, to scrape oil the discharged fluxed and milled material. The plow scrapers 54, 55 are particularly useful with thermosetting materials such as phenol aldehyde and ureaaldehyde resins which tend to stick to roll surfaces. Alternatively, rotary cutters 51, 58 may be used (particularly with thermoplastic vinyl materials which release more readily than thermosetting material from roll surfaces) to cutoff milled material of definite width, providing a pull is exerted on the cut material to assist its release from the smooth annular surfaces 5 l, 52.

In the operation of the apparatus embodiment of Figs. 1 to '7, powdered material is fed to the threaded rolls 2|, 22 from a feed hopper located over a central opening above the junction of the dual threads of each roll 2|, 22. Preferably the feeding is continuous. Upon coming in contact with the threaded rolls 2 I, 22, the powdered material is drawn into the downward bite of the threaded rolls 2|, 22 and then while being conveyed towards the discharge surfaces 5|, 52 of the rolls, is repeatedly drawn through the bite of the rolls.

Some powdered material falls through the radial clearance in the zone of intermesh of the threaded rolls 2!, 22 and is deposited on the floor ing through the radial clearance is fiuxed and milled by repeated passage through the bite of the rolls. The frictional heat developed in milling as well as heat supplied by heating fluid introduced into cores d8, as of the threaded rolls 2!, 22 initiates rapid fiuxing of the meltable substances in the powdered material. The fluxed material adhering to the threads and being repeatedly drawn through the bite of the rolls picks up some of the powdered material lying on the floor of the lower saddle plate 29 and pushes the remainder unaltered in a direction towards the annular surfaces of revolution 43, id, 56, 41, associated with the insert barriers i0, 4!. Within the devious passageways between the barriers 30, M and the rotating annular surfaces of revolution 43, 54, dd, the mixture of fiuxed and unfluxed powder is subjected to intense pressures, shearing actions and tortuous fiow. The combinations of these actions effectively mixes all the powdered material into a completely fiuxed plastic mass devoid of unwetted nonmeltable substances (such as pigments or fillers) or of unfluXed resin particles. The fluxed mass upon emerging from the tortuous passage is then subjected to further milling action by the threaded rolls El, 22 before discharge onto the smooth discharge surfaces 55, 52 of the threaded rolls 2 I, 22. The milled material is removed from the smooth roll surfaces 5!, 52 by rotary or scraper knives as shown in Figs. 3 and 4 respectively.

Peripheral speeds between 60 and 180 feet per minute, for example by rolls of 6 inch pitch diameters are satisfactory for processing many types of plastic materials, such as the vinyl resins and thermosetting phenolic resins. Higher rota tional speeds are feasible but require more driving energy, while lower speeds require less driving energy but with lower production rate of milled material. Similarly, but to a lesser extent, close radial clearances in the zone of intermesh between the threaded rolls 2!, 22 (for example 0.005 inch) reduce the milling production rate, while larger radial clearances (for example 0.040 to 0.100 inch) increase milling production.

In the embodiment of Figs. 8 and 9 the annular surface of revolution 6! is in the mid-l ngth of a driver dual-threaded roll 62 (and is correspondingly located on the intermeshing driven roll not shown in Fig. 8). The annular surface of revolution 5! is essentially a smooth cylindrical surface. Associated with the cylindrical surfaces SI of these rolls are two pairs of semi-annular saddle plate inserts fi l. 12 having several parallel semi-helical barriers cc separated by grooves M3.

The grooves iii between the semi-helical barriers 69 have smooth base floors. The barriers 69 and the grooves '50 of each insert pair meet each other at the bottom half of the inserts G4, 12 but are separated at the upper half to provide an opening for powdered material to enter into the bite between the smooth annular surfaces of revolution 6! on each of the threaded rolls.

The right hand pair of the semi-helical type inserts Ed is shown in perspective detail in Fig. 9. The direction of the spiral barriers 69 is such as to convey material to the dual threads on the right side of the apparatus when the rotation of the intermeshing threaded rolls is such as to effect a downward bite on material being milled. The left hand pair of semi-helical type inserts 72 has its semi-helical barriers it in a diametrically opposite direction to that of the right hand insert 62 whereby the former directs powdered material to the left side of the apparatus. The radial clearances between the smooth cylindrical surfaces of revolution BI and the spiral barriers 69, 13 of each insert 64, I2 are closer to mechanical clearances than in the previous embodiment in order to delay the conveying of material, and favor repeated milling of material between the smooth annular surfaces of revolution Bl on the rolls.

The milling and fiuxin of powdered mat rial in the a aratus embodiment of Figs. 8 and 9 starts with introduction of powdered material into the nip or bite between the mating smooth cylindrical surfaces SI of the threaded rolls. Some of the powder is immediately fluxed and adheres at once to the smooth roll surfaces 5| to form a rolling bank of fiuxed material. The remainder of the owder falls through the bite between the smooth cylindrical surfaces 6| and is deposit d in the grooves iii, M between the semi-helical barriers as, it. As fluxed material builds up on the smooth roll s rfaces 6 i. it makes contact with the semi-helical barriers 69, it and is continuously pushed and guided thereby helically across the smooth roll surfaces 5! towards the intermeshing screw threads of the rolls. In the meantime unfluxed powdered material accumulates in the grooves W, M between the spiral barriers E9, 13 until it attains a high enough level to make contact with the fluxed mass adhering to the smooth surfaces 6! on the rolls. Upon contact with the fluxed portion, the powdered material is picked up and masticated therewith on entering the bite of the smooth rolls and the resultant plastic mixture gradually is dis laced.

onto the screw threaded portion of the rolls.

The embodiment shown in Fig. 10 is a combination of the two modificationsp-reviously illustrated and described. It comprises intermeshing dual threaded rolls, each having, as is illustrated for the driving roll E8 in Fig. 10, a smooth central annular or cylindrical surface of revolution l9 and interposed in each of the dual threads a v-shaped annular surface of revolution 82, 84. A pair of semi-annular inserts having semi-helical barriers {iii and BI of the type shown in Fig. 9 confines, except for a feed opening, the central smooth annular surfaces of the revolution 13 on the roll '38. The V-shaped annular surfaces of revolution 82, 8d rotate within a groove provided between V-shaped semiannular barriers in a pair of inserts of the type illustrated in Fig. 6.

In the embodiment shown in Fig. 11, semi-helical barriers 8i and semi-annular barriers 89 are formed integral with the upper and lower saddle plates. The mixing and milling action is the same as occurs in the embodiment of Fig. 10. The integral type of barrier construction dispenses with the joints inherent with the insert type of barriers into which plastic material may lodge if the machining of the inserts and correspondin recesses in the housing is not of precision accuracy. On the other hand, the integral type of construction is more machine and involves greater replacement cost upon ultimate wearing of the barriers.

The milled material discharged from any of the embodiments of the continuous milling apparatus may be removed therefrom as a continuous flat sheet as illustrated in Figs. 3 and 4. Dther continuous shapes free from undercuts are also feasible. for instance a ribbed shape as illustrated in Fig. 13 is obtained by annular recessed surfaces on the discharge end of the threaded rolls as illustrated in Fig. .12.

expensive to g We'cIaim:

1. Apparatus for fluxing and milling plastic material comprising in combination a pair of parallel rolls having intermcshing leftand right-hand screw threads with a radial clearance in the zone of intermesh in excess of mechanical clearance to form a bite for milling the plastic, the screws threads of each roll being interrupted by at least one non-helical annular surface of revolution, said annular surfaces mating with each other and having clearance therebetween in the mating area in excess of mechanical clearance for milling the plastic a housing closelyconiining said rolls, arcuate barriers projecting from said housing toward each of said anm suiu aces of revolution and encircling the major portion of such annular surfaces to form therev l devious arcuote passageways in which the plastic 111a 'ial fiuxed and milled.

2. Ap aratus for fiuxing and milling plastic material comprising in combination a pair of parallel rolls having intermeshing leftand right-hand V -shaped screw threads with a radial clearance in t--e zone of interrnesh in excess of mechanical clearance to form a bite for milling the plastic, at least one non-helical surface of revolution interrupting the a threads of each roll and having a diameter less than the outer diameter said screw threads, the nonhelical surface on one roll mating with the nonhelical surface on the other roll to provide a clearance therebetween at the mating area for millin the plastic a housing closely confining said rolls, individual barriers projecting from said housing toward each of said annular surfaces of revolution, each barrier encircling a major portion of one of the annular surfaces to form therewith devious passageways in which the plastic material is fiuxed and milled. V

?. Apparatus for milling and fiuxing plastic com in combination a pair of rolls having intermeshing leftand of '-shap-e in axial for a maior portion of the length 'ith a. rad. .l clearance in the zone in excess of mechanical clearance into for rn" form a to e, a nonthread d annular c of i. V-

iap? cross-section opting the sore .l of said rolls 11;. having a diam than the diameter of sc v. being a adial plastic, a

bore closely each bore projectin from two. the

the encompass'r the annular s in the spaces with clearance therebetween in excess of mechanical clearance for fluxing the material therein.

4. Apparatus for milling and fiuxing plastic material comprising in combination a pair of parallel rolls having intermeshing leftand i he in .lar

roll confined with l a major portion said surface,

1 of revolution rotating with" right-hand screw threads of a V-shape in axial cross section for a major portion of the length of rolls with a radial clearance in the zone of intermesh in excess of mechanical clearance to form a bite for milling the plastic, a nonthreaded smooth annular surface of revolution interrupting the screw threads of each of said rolls and mating with each other to form a milling bite for the plastic material, a housing having a smooth-wall dual bore closely confining said rolls, semi-helical barriers projecting from said housing wall and associated with a major circumferential area of the non-mating portions of said surfaces of revolution to provide a clearance therebetween for millin the plastic material.

5. Apparatus for conveying and milling plastic material comprising in combination a pair of dual screw threaded parallel rolls, each roll having intermeshing leftand right-hand screw threads of a V-shape in axial cross-section for a major portion of the length of the rolls with a radial clearance in the zone of intermesh in excess of mechanical clearance to form a bite for milling the plastic, a non-helical annular surface of revolution interrupting each of the leftand right-hand threads of each roll, a housing having a smootlnwall dual bore closely confining said rolls, the annular surface of one roll being positioned adjacent the annular surface of the other roll with a clearance therebetween for milling the plastic, and adjacent to each surface of revolution a se1ni-circumferential barrier projecting from said housing wall toward said surface of revolution and encircling a major circumferential portion of said surface to form therewith a passageway for fluxing and milling the plastic material.

6. Apparatus for milling and fluxing plastic material comprising a pair of parallel rolls having interme hing left and right-hand screw threads of a V-shape in axial cross section for a major portion of the length of the rolls with a radial clearance in the zone of intermesh in excess of mechanical clearance to form a bite for milling the plastic, mating grooved annular surfaces on the ends of said rolls, a non-helical annular surface of revolution interrupting the screw threads of each of said rolls said nonhelical surfaces mating with each other with a clearance therebetween at the mating surfaces for milling the plastic, a housing having a smooth-wall dual bore confining said rolls, semiannular barriers projecting from said housing wall toward said surfaces of revolution and substantially enclosing the non-mating areas of said surfaces to provide a passageway therebetween for milling and fluxing the plastic material.

HERBERT A. SWALLOW. HENRY H. ANDERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,935,050 Gordon Nov. 14, 1933 2,43%,707 Marshall Jan. 20, 1948 

